The humble proton may seem simple enough, and they’re certainly common. People are made of cells, cells are made of molecules, molecules are made of atoms, atoms are made of electrons, protons, and neutrons. And protons are each made of three up or down quarks. Simple stuff, right? All except for that last part. Protons are actually made of many, many quarks that happen to look like three only when we look at them in a particular way. And even then, sometimes they’re made of 5 quarks - including the charm quark.
